This is an investigation of pathological and physiological factors affecting regional cerebral blood volume (rCBV). rCBV is measured by detecting with a semiconductor radiation detector the stimulated x-ray fluroescence of a high atomic number indicator injected intravenously. The studies carried out are (1) correlation of rCBV with other regulatory factors in the control of cerebral hemodynamics (paCO2 and arterial blood pressure). (2) Study in rhesus monkeys of the effect of metrazole-induced seizures on rCBV and mean transit time. This study also involves the combined effects of hypertension and hypercapnia and of elevated intracranial pressure on rCBV. (3) Correlation between rCBV in normal human subjects and in patients with pseudotumors and dementia. (4) Instrument developments in an attempt to maximize the fluorescent signal from the brain with respect to flurescence originating in extracranial tissues. (5) Development of high atomic number indicators for fluorescent studies.